Method of degasifying liquid for electrical insulating purposes



2 Sheets-Sheet 1 Hqt on Filed Feb. 1, 1939 C. A. PIERCY ET AL Tan Vacmum Degasii ing METHOD OF DEGASIFYING LIQUI D FOR ELECTRICAL INSULATINGPURPOSES lnvenccn s'. CaH A. Fievcg, Eugene L.C1r-a1nda\l, by 1 TheirAttorney.

May 21, 1940. c. A. PIE RCY ET AL 2,201,870

METHOD OF DEGASIFYING LIQUID FOR ELECTRICAL INSULATING PURPOSES FilgdFeb. 1, 1939 2 Sheets-Sheet 2 Fig.3. Z/

Fig.4.

2a EEG-L --Zo :CD 31) zr 24 Inventors:

Carl A. Piercg, Eugene L. C'rahdaH, 5

- Then Actor'heg Y 25 um and in increasing its acid value.

' Patented May 21, 1940 er ris METHQD F DEGASIFYING LEQ FOR ELECTRICALINSULATING PURPQSES Carl A. Piercy, Ballston Lake, andv Eugene L.

Crandall, Scotia, N.

in, assignors to General Electric Company, a corporation or New YorkApplication February 1, 1939, Serial No. 254,006

4 Claims.

Raw oil is very largely used as an impregnating medium to improve thedielectric strength of insulating material, such as paper for example.Such oil, after being carefully refined by exist- 5 ing methods toremove impurities, contains approximately 12% by volume of air and othergases, and is satisfactory for many electrical purposes but not forcable intended to carry high tension current, for exarnple of the orderof 132,000 volts and upwards. As a result, it has been the practice todegasiiy the oil to remove the contained gases, and to maintain it insuch condition during its introduction and utilization as an impregnant.

For degasiflcation, the prior practice has been to initially andcontinuously heat the raw oil to a substantial degree and while soheated to subject it to the effects of vacuum to facilitate theliberation of the contained gases. We-have 20 determined that theinitial and continued application of heat in this manner throughout theprocess results in reducing the resistivity of the oil to the passage ofelectric currents; in increasing its power factor as an insulating medl-These changes in the oil are accompanied by a change of color.

A seriousobjection to the initial and continuous use of heat throughoutthe entire cycle, as in the past, is that it is liable to cause burningof the oil to a greater or less extent, particularly at the beginning ofthe cycle, thereby resulting in serious damage to. the electricalapparatus in which it is used. This isdue largely or wholly to the factthat cold oil is introduced into an empty tank which because it is emptymay have a higher temperature than it should have. The damage due toimproper heating is not readily ascertained because the operations arenecessarily carried out in a closed system and the degasifled oil takenfrom such system isv delivered to the apparatus in which it is usedwithout lie-- ing subject to suitable or visual inspection.

In brief, the changes in the oil brought about by initially andcontinuously heating it during degasification decreases its insulating"value, the

amount of such decrease depending upon various factors including thekind of apparatus used and the skill of the operators performing thework.

It has also been the prior practice to recirculate the .oil within thesame tank in which it is heated, as for example by taking oil from thebottom of the tank and discharging it into the 55 top thereof, meanwhilemaintaining the tank This means that the circu-' Tanks for this purposeare relamethod of degasifylng oil or other liquid for use as aninsulating material in electrical apparatus.

In carrying out our improved method, the major part of the containedgases are removed from the 011 while it is in a cold state, i. e., at

7 approximately room temperature whereby objectionable changes in thecharacter of the oil are obviated. This is done by subjecting the coldoil in a cold degasifying tank or container to a vacuum and continuouslyremoving the oil as it is degasified and conveying it to another vacuumtank where it is temporarily retained.

This last mentioned tank for convenience may be termed a storage tank.To more eflectively remove the gases during the vacuum treatment, whichmay be termed the cold stage of the process, the oil is caused to passinto the tank through suitable devices which discharge it in the form ofa spray or sprays, thereby greatly increasing the surface of area of theoil exposed to'the vacuum. Subsequently in what may be v termed the hotstage of the process, the relatively small remanents'of such gases arewithin practical limits removed by subjecting the oil to heat as byheating the tank or container and spraying the oil into the heatedvacuum. tank. The oil is continuously removed from the last mentionedtank and conveyed to a suitable vacuum storage tank. Heat may beimparted to the oil after it has had the greater portion of itscontained air removed with practically no danger of injury because ofthe absence of any substantial amount of oxygen therein. This isparticularly true where the process as in the present case separateswhat may be termed the cold stage of the cycle of operation from the hotstage."

Stated more specifically, the cold oil is continuously delivered asthrough suitable spray means into what for convenience may be termed adegasifying tank. Now instead of circulating the oil over and over againon itself in the degasifying tank, the largely degasifled oil iscontinuous- 1y removed from the degasifying tank and conveyed to anotherevacuated storage tank from which 011 is withdrawn for the hot stage ofthe process. In the event that degasification of the cold oil by asingle pass through the degasifier tank is not suflicient for aparticular use, the operation may be repeated one or more times. By thisarrangement of immediately separating degasified oil from that whichcontains a greater amount of gas, the length of time required for theprocess may be reduced as much as threequarters over the priorprocedure. If the degasification of the hot oil by a single pass is notsufficient, the operation may be repeated one or more times.

For a consideration of what we believe to be novel and our invention,attention is directed to the accompanying description and the claimsappended thereto.

In the accompanying drawings is illustrated apparatus suitable forcarrying out our invention in which Fig. l is a diagrammatic view ofsuch apparatus; Fig. 2 illustrates the portion of the apparatus which isactive during the second pass of cold oil through the degasifying tank;Fig. 3 illustrates the portion of the apparatus which is in active useduring the first hot cycle or stage of operation; Fig. 4 illustrates theportion of the apparatus which is in use during the second hot or finalstage of degasification; Fig. 5 is a detail view of the degasifying tankcontaining the spraying apparatus, and Fig. dis a detail view of thetank in which heat is imparted to the oil.

I0 indicates a vacuum tank to which raw or untreated oil is admittedfrom a suitable source of supply, such as tank II, by the pipe l2,subject to the control of a valve 3. N indicates a sealed storage tankof suitable size to receive and retain the charge of degasified oilultimately received from tank Ill. Tank I4 is maintained under vacuum bya pump as will appear later, through the pipe I 5 having a controllingvalve I8. I! indicates a tank in which the oil is heatedduring-the'second or hot stage of operation of the method. Theconstruction of this tank is shown more in detail in Fig. 6. The tank issealed and contains top and bottom headers or tube sheets IS in whichthe tubes I9 are secured at their respective ends. The space between theseveral tubes and the wall of the tank contains a body of oil 20constituting an oil bath, said oil being separate from that undergoingtreatment. Connected to the oil bath by a pipe 2| is an expansion tank2| to take care of expansion of th oil when heated. The oil bath issuitably heated, as for example. by a coil of pipe 22 to which steam isadmitted by the inlet pipe 23 and withdrawn by the outlet pipe 24. Whenit is desired to cool the tank, the supply of steam is shut ofl from thecoil 22 and cooling water caused to flow therethrough. The temperatureof the oil bath may readily be controlled by regualting the pressure andtmeperature of the heating steam. Other forms of controllable heat forthe tank may be employed. Because in the first stage of operation theparts should be cold. meaning thereby that they should be at or aboutroom temperature, the coil 22 after the steam is shut oil by suitablevalves is supplied with properly circulated cooling water. Thisarrangement avoids the use of a separate cooling coil although such acoil may be employed if desired. The main consideration is that the oilto be treated should be cold in the first stage or operation and hot atthe later stage. Care should be exer-. cised to reduce the temperatureof the heating tank before the succeeding charge of raw oil is admittedto the apparatus.

25 indicates a sealed tank, for convenience termed the degasifying tank,containing as shown in Fig. 5 one or more spray nozzles 26 and bafiler21 for each nozzle. The oil contained in the tank 25 when undergoingtreatment during the second stage of operation is heated by the steamcoil 28, steam being admitted by a suitable inlet pipe 29 and dischargedby a suitable outlet pipe 30. In order to cool the tank for the firststage operation or operations, cold water is circulated through the coilafter the steam is shut oif for the same reasons indicated in connectionwith tank I1 and by similar means. The tank 25 has an expansion tanksimilar to tank 2| of Fig. 6 and for the same purpose.

3| indicates a vacuum pump which is connected to the tanks l0, l4 and 25by the main pipe 32 and suitable branch pipes. some or all of the latterhaving shut off valves. The oil being treated is circulated byseparately driven pumps 33 and 34 which may be of any suitableconstruction provided they do not admit air to the system. In order toprevent excess pressure in the system due to the circulating pump 33, abypass 35 is provided between the discharge side of the pump and thesupply'tank ||l containing cold raw oil. In this by-pass is located aloaded relief valve 36 of any suitable construction which opens towardthe tank Ill when thevprecletermined pressure is exceeded. A valve 3'!permits shutting off the passage of oil from the by-pass to the tank l4.As will appear later on, the pump 33 first circulates raw oil and thendegasified oil. The same is true of the circulating pump 34. Thecompletely degasified oil is removed from the apparatus by the outletpipe 38 subjected to a control valve 39. In the delivery pipe 40 of thecirculating pump 33 is a suitable pressure gauge 4|. The vacuum pump 3|and the degasifying or spraying tank 25 are both provided with vacuumgauges 42 which may be of the U-tube or other type.

Assuming the tank I0 is to be filled or substantially filled with oil orother liquid and valve 31 closed, it is fed to the pump 33 by the pipe43 subject to the control of the valve 44, the valve 50 being closed.-From the pump, oil flows through pipe 40 to the sprays 26 in the tank25. At this stage in the process, the tank 25 is kept cool bycirculating water through the coil 23, Fig. 5, and evacuated by pump 3|.From the tank 25, the oil from which the major part of the gases hasbeen removed is fed to the vacuum storage tank |4 by pump 34 and pipe45, the heating tank being shut on by valves 53 and 53. The tanks I4 and25 are both connected by the pipe 32 to the vacuum pump 3| which iscontinuously operated. The pumps utilized are desirably operated byelectric motors in the usual way subject to necessary controlling means.The capacity of storage tank I4 is desirably great enough to receive andretain the amount of oil originally contained in tank I0. During thisstage or part of the process or method, the amount of gas contained inthe raw oil is advantageously reduced to a small value, say 1% by volumeas contrasted with approximately 12% contained at. the start. The figureof 1% is not a definite one but is given by way of illustration, alimited variation being permissible. Shou d it be desired, cold oil Ymay be caused to flow or pass a second time through the cooled vacuumtank 25 for the purpose of further removing its contained gases.

, This is not always necessary but is desirable in off valve 53 into thetank ll.

some cases. Assuming that the oil after the first pass is contained instorage tank It, for a second pass it flows therefrom by pipe 5|, Fig.2, through open valve 50 to the pump 33, the valve 44 being closed toshut off tank I0. Oil from the pump flows through pipe-40 to thedegasifying tank 25 which at this stage is cold or at room temperature.The oil after having been sprayed by the nozzles 26 collects in thebottom of the tank and is fed by the pump 34 through shut- The coldstageof the treatment ends when the oil leaves the tank 26. The tank I!is heated and at this point the hot stage of the process begins. As theoil flows through the tank, it is heated by the steam coil 22 of Fig. 6and flows through pipe 54 into tank l0 which initially contained rawoil, the valve 44 in its outlet pipe 43 being closed.

In Fig. 3 is indicated the portions of the apparatus in active useduring what may be termed for convenience a hot stage of the process.During this stage, a suitable temperature for the oil being treated isbetween 90 and '100 C. due'to the action of heating tank ll. Deslrably'in no part of the method at any time is the temperature of the oilpermitted to exceed 105 C.,

'any contained air or moisture.

and the nearer it is maintained within the limits of 90 to 100 0., thebetter will be the final results. In thisflgure, the tanks 51 and 25 areboth heated, as by passing steam at the desired controlled temperaturethrough their respective heating coils, as before explained. All threeof the pumps 3!, 33 and 34 are active and at this stage or step in theprocess, the oil after it is heated in tanks 25 and II flows into thestorage tank I which as previously indicated is continuously under avacuum and which previously contained partially degasified cold oil. Thearrows indicate thepassage of oil from the tanks I0. 25 and I1 into thetank M. As above stated at this stage of the process, the oil is hotwhereas in the earlier stage, it was cold.

In Fig 4 is illustrated the active parts during the final stage of theprocessin which the degasified hot oil is contained in storage tank I4.Assuming the tank ll to'have been filled .by the preceding step, thevalve 51 in the inlet pipe discharging into the tank is closed as isalso the valve 50 in the pipe leading. to degasifying tank 25. The valvein the pipe 5| leading from the tank It to the suction side of the pump33 is opened. A suitable connection is made from the discharge pipe 38to the container designed to receive the degasified oil and valve 39 isopened. In making the connection between pipe 38 and the container toreceive the oil, it is desirable to permit a limited amount of oil toescape to free the pipe beyond the valve of The circulating pump 33which had been temporarily stopped while the various valves were beingmanipulated is now in operation and degasifled oil is pumped through thecoils so as to reduce the temperature of the tanks to approximately roomtemperature preparatory to receiving a new charge of raw oil. By thismeans the degasified oil entering the storage tank It mayhave itstemperature reduced. No attempt has been made in the drawings to showthe relative sizes of the tanks or their respective positions sincethedrawings are of a diagrammatic nature in order to more clearlyillustrate the steps in the process. The sizes of the tanks and theirrespective positions. the pumps, valves, etc. should, of course, followgood engineering practice.

From the foregoing, it will be seen that in the cold stage of theprocess, raw oil is taken from the cold tank It and conveyed to the colddegasiiying tank 25 where a major portion of the ases are removed byvacuum, and that instead of being'recirculated on itself, as was theprior step in the operation removes all or practically all of the hotdegasifled oil from the tank it which initially contained raw oil, anddelivers it to vacuum tank it. Prior to delivering the fully degasifiedoil to the tank 08 in the last stage of the process, it may be cooled bycirculating water about the tank il. Having filled tank it, the oil isremoved for use by the par= ticular parts shown in Fig. 4. It is to beparticularly noted that at no time is the raw oil sub jected to anamount of heat sullleient to injure it because of its contained air. Itis recognized. of course, that even with the cooling coils, there may bea small amount of heat retained by the parts of the tanks. It is onlyafter the major part of the gases, particularly air, have been removedfrom the oil that it is subjected to an appreciable amount of heat.

The tanks H and 25 are each provided with an inlet pipe and valve forcontrolling admission of oil to the oil bath, and a valve controlleddrain pipe 61: We have illustrated tanks I! and 25 as imparting heat tothe liquid by steam coils which surround them but other means may beemployed for the purpose. We have also illustrated means for cooling thetanks. The main consideration is to provide controllable means M hod rdr Il tielecgttrlilc Resistivity A 9, M l ct o egasi ylng 8 ran 0 msperkv. at 40 C. cmJX 10" color Old roeess:

elore degas 30 50 1.3 After degss 32 g 17 1.10 Our process:

Before degas 30 41. 7 1. 4 After degas. 35 41.7 1.4

The gas content as measured in the oil degasifled according to thepresent process averages and from it to the vacuum storage tank It. This0.2% by volume. The color numbers are those of the American Society ofTesting Materials, National Paint Association.

Reference has been made to the degasiiication of oil because of itsextensive use as an insulating fluid but other liquids used for the samepurpose may be degasified in the same manner.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. The method of degasii'ying liquid to improve its insulatingproperties which comprises supplying cold raw liquid to a supply tank,continuously removing the liquid from the supply tank and spraying itwhen in a cold state into a cold tank where it is partially degasified,continuously removing the partially degasified cold liquid from thedegasifying tank and temporarily delivering it to a storage tank,maintaining a vacuum in both of said tanks, continuously removing thepartially degasified liquid from the storage tank and passing it intoand through a heating tank for heating the liquid, continuously removingthe liquid from the heating tank and returning it in its heatedcondition to the original supply tank, continuously removing heatedliquid from the supply tank and delivering it for a second time to thedegasifying tank, heating the degasifying tank to assist in liberatinggas from the liquid, removing the heated degasified liquid from thedegasifying tank and delivering it for a second time to the storage tankfrom which it is withdrawn for use and subsequently cooling thedegasifying tank and the heating tank preparatory to admitting a secondcharge of raw liquid thereto.

2. The method of degasifying liquid to improve its insulating propertieswhich comprises suplying cold liquid to a supply tank, removing theliquid from the supply tank and spraying it in a cold state into a colddegasifylng tank where its contained gases are largely removed byvacuum, removing the largely degasified liquid therefrom and deliveringit to a cold storage tank where it is temporarily retained, maintaininga vacuum in both of said tanks, removing the largely degasified coldliquid from the storage tank and passing it into and through a heatingtank where the liquid is heated, removing the heated liquid from theheating tank and returning it to the original supply tank, removing theheated liquid from the supply tank and delivering it for a second timeto the degasifying tank where it is sub-' jected to the effects ofvacuum, supplying heat to the degasifying tank to facilitate removal ofgas from the liquid, removing the heated degasified liquid from saidtank and delivering it for a second time to the cold storage tank,removing the liquid for use from the storage tank without exposing it tothe effects of the atmosphere, and subsequently cooling both thedegasiiying tank and the heating tank preparatory to admitting a secondcharge of liquid to said tanks and to the supply tank.

. 3. The method of degasifying liquid to improve its insulatingproperties which comprises supplying cold raw liquid to a supply tank,continuously removing the liquid fromthe supply tank and spraying itwhen in a cold state into a cold degasifying tank where it is largelydegasified, continuously removing the largely degasified cold liquidfrom the degasifying tank and temporarily delivering it to a storagetank, maintaining a vacuum in both of said tanks, continuously removingthe largely degasified liquid from the storage tank and passing it intoand through a heating tank for heating the liquid, continuously removingthe liquid from the heating tank and returning it in its heatedcondition to the original supply tank, continuously removing heatedliquid from the supply tank and delivering it for a second time to thedegasifying tank, heating the degasiiying tank to assist in liberatinggas from the liquid. removing the heated degasified liquid from thedegasifylng tank and passing the hot liquid from the degasifying tankthrough a cooling tank for reducing its temperature, delivering theliquid for a second time into the storage tank from which it is removedfor use, and subsequently cooling the degasifying tank preparatory toadmitting a second charge of raw liquid thereto.

4. The method of degasifying insulating liquid to improve its insulatingproperties which comprises supplying cold raw liquid to a supply tank,continuously removing liquid from the supply tank and by a first pumpspraying it in a cold state into a cold degasifying tank wherein it islargely degasified, continuously removing the so degasified liquid fromthe tank and by a second pump delivering it to a storage tank where itis temporarily retained, maintaining both tanks under vacuum,continuously removing the largely degasified liquid from the storagetank and by the first pump returning it to the degasifying tank for asecond pass therethrough, continuously removing liquid from thedegasiiying tank by the second pump and causing it to pass through aheating tank and thence into the original supply tank, continuouslyremoving hot oil from the supply tank and by the first pump returning itto the degasifying tank, heating the degasiiying tank, continuouslyremoving hot degasified liquid from the tank by the second pump anddelivering it to the storage tank, and withdrawing degasifled liquidfrom the storage tank by the first pump and delivering it to an outletpipe for subsequent use.

CARL A. PIERCY. EUGENE L. CRANDALL.

